1. Field of the Invention
The invention relates generally to a differential mechanism, which transmits rotating power to the wheels of a motor vehicle and locks to prevent the wheels from rotating at different speeds.
2. Description of the Prior Art
It is conventional to use an open or limited slip differential mechanism to permit limited wheel slip at a vehicle axle, i.e., to produce a rotational speed difference between the driven wheels. A purpose of a locking differential is to prevent relative rotation of one driven wheel with respect to another driven wheel. This is usually accomplished by locking one differential side gear to a differential case, thereby preventing rotation of the side gear with respect to the differential case, and preventing relative wheel speed differentiation across any one axle.
A locking differential can also be used as an inter-wheel differential or as a center differential in 4×4 and AWD vehicles. In this case, the axis of the differential assembly is parallel to the longitudinal axis of the vehicle. The center differential allows drive shaft speed differences between the front and rear axles. But there are some cases where it is desired to lock the front and rear axle drive shafts together such that a single rotation speed is re attained. This condition is known as a locked center differential.
When activated, an electronically locking differential uses a voltage source to produce a magnetic force that overcomes a reactionary spring force applied to a locking ring (mechanical engagement mechanism), thereby mechanically coupling a side gear to a differential case through the lock ring. When activated, the electronic locking differential prevents relative speed differences between the controlled wheels.
If the electronic locking differential is required to function at low voltage and high coil temperature without a temperature compensation strategy, then the electromagnetic hardware, including wire and the coil winding, must have a relatively large size in order to produce a magnetic actuating force that is able to overcome the spring force. The spring force must be set high enough to prevent partial engagement of the lock ring to the side gear during all dynamic vehicle operating conditions.
A need exists in the industry for a control strategy that enables functionality of the electronic locking differential on all road and off-road surfaces, axle fluid temperatures and coil temperature while minimizing the size of the electronic actuating locker hardware.